1. Field of the Invention
The present invention relates to an optical disk apparatus, more specifically to the type which record/erase data on/from an optical disk having a plurality of tracks grouped into a plurality of zones arranged in its radial direction, using a particular frequency clock for a different zone.
2. Description of the Related Art
Optical disks are formatted in advance for achieving a large storing capacity, reproduction of data accurately from a target address, and storage of data accurately into a target address. There are two known formatting modes, i.e. the CLV (constant linear velocity) mode in which the rotation of the motor is controlled in inversely proportional to the radius of the track, and the track is followed at a constant linear speed at all times, and the CAV (constant angular velocity) mode in which the rotation of the optical disk is set at constant.
As compared to the CLV mode, the CAV mode provides an easier control of the motor which rotates the optical disk; however, entails the problem of a small memory capacity. In order to increase the memory capacity of the optical disk as the CAV mode, the Z.multidot.CAV (zone constant angular velocity) mode or the M.multidot.CAV (modified constant angular velocity) mode is used as a further formatting method. In either the Z.multidot.CAV mode or the M.multidot.CAV mode, an optical disk is divided into a plurality of zones each formed of a plurality of tracks arranged in its radial direction. Each zone has the same number of selectors per one track within that zone, and a different zone has a different number of selectors per one track. According to the Z.multidot.CAV mode, when data is stored onto an optical disk or reproduced data therefrom, the optical disk is rotated at a constant 10 speed, and the storing or reproducing operation is carried out by using an optical head with reference to a particular frequency clock which is different from one zone to another. More specifically, each time the optical head accesses a track of a different zone, the reference clock frequency is renewed. Then, data is stored in the track, and the data is reproduced from the track.
When an M-CAV formatted optical disk is installed in an optical disk apparatus, the apparatus needs to interrupt data-recording, data-reproducing or data-erasing operation for some time whenever any zone of an optical disk is switched to the adjacent zone of the optical disk in order to record data in, reproduce data from, or erase data from, a track of the adjacent track. While the disk is being rotated one turn after the data-processing operation has been interrupted, the frequency of the master clock signal used is altered and stabilized. Namely, the optical disk apparatus has a wait time approximately equal to the time the disk requires to rotate 360.degree.. Within this wait time, the frequency of the master clock signal is stabilized, whereby data can thereafter be recorded in, reproduced from, or erased from, a data section of the newly selected zone. Due to the wait time, the conventional optical disk apparatus cannot record, reproduce or erase data continuously. Its operating speed is inevitably 10 low.